To circumvent radionuclide accumulation in nontarget tissues when employing metallic radionuclides for radioimmunoscintigraphy or radioimmunotherapy, we have investigated the effect of the chelating agent deferroxamine (DFO) on the biodistribution of 6 7 Ga following its administration attached to intact monoclonal antibody MAb35 and its F(ab ) 2 fragment. Following administration of 6 7 Ga-labeled MAb35, DFO accelerated whole-body elimination of 6 7 Ga and reduced its accumulation in several normal tissues, including liver, spleen and kidney. No reduction in tumor accumulation of 6 7 Ga was observed. Following administration of 6 7 Ga-labeled F(ab ) 2 fragment, kidney accumulation was higher than with the intact antibody (29% and 4% ID/g, respectively) and blood levels lower (0.69% and 5% ID/g, respectively). Again, no alteration in tumor accumulation of 6 7 Ga was seen following DFO, although liver, kidney and blood levels were reduced and whole-body elimination accelerated.